1. Technical Field
The invention relates to a mode filter for connecting two electromagnetic waveguides with different cross-sectional shapes, which has a tubular section with openings at both ends. The cross-sections of the openings correspond to the respective cross-sections of the two different waveguides. The interior space of the tubular section changes over smoothly from one cross-sectional shape to the other. In the interior space of the tubular section, there are also arranged means for minimizing unwanted modes of the modes of propagation to be transmitted.
2. Description of the Prior Art
Waveguides exhibit low damping of transmitted electromagnetic waves, in particular at higher frequencies, and are used, for example, as feed lines for antennae. However, the damping can still be too high, for example, if the transmitted power is low or if large enough reflectors cannot be utilized. The waveguides can then be used overmoded, i.e. operated at higher frequencies than the design frequency. In this case, however, undesirable higher modes are then excited in the waveguides in addition to the desired fundamental mode. This causes ripples in the group velocity and in the amplitude of the fundamental mode, i.e. a variation of the amplitude of the fundamental mode. This effect cannot be completely eliminated; it can, however, be minimized by employing mode filters.
A mode filter of the type described above is distributed by the company RFS kabelmetal, Hannover, Germany. Such a mode filter decouples the undesirable modes. For this purpose, baffles are arranged on the wall of the mode filter which is in the form of a tubular section. The baffles are connected to absorbers attached on the outside of the tubular section. The absorbers are cooled during operation.